Always do the math analysis and try to look at all properties if you have the time to look at prospective properties before you make an offer or at least have a clause in the sales contract that allows you the time (about 10 days) to make a detailed inspection on the prospective property and possibly get out of the deal without a penalty that will hurt you too much.Do not try to do everything yourself.  

this is the first time I heard of that.Most sales contract have attorney reviews.

Think about that later (I'm not a lawyer, so this isn't legal counsil, but LLCNext steps: REVIEW those leases!

If they own several they are obviously investors.Once you get a response from the seller of the vacant house, negotiate a deal to buy it for all cash and get it under contract.

Yes Was the job done as in the contract  ?      

I'm new to real estate investing and would like to know if before going into a contract or start looking for rehab deals do I need to first get prequalified by a hardmoney lender and get that letter to provide to agents or they want a deal under contract first?

Whether guilty or not, the legal fees and time involved would not be pleasant. 

Pulling comps, filling out contracts, entering data into CRM and deal analyzer tools, organizing contractors and general logistical paperwork and phone calls. 

I suggest you to be properly acquire instructions and knowledge of the 'legal' ways to be involved.

However, it will all comedown to what you negotiated into the contract.